Hydrocarbon fluids such as natural gas and oil may be obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing geologic formation. In many types of subsea applications, a wellhead is positioned at a sea floor above a wellbore drilled down into the subterranean geologic formation. A subsea tree system is mounted on the wellhead and both the subsea tree system and the wellhead have an internal passage through which various well equipment may be deployed. A seal is positioned between the subsea tree system and the wellhead to ensure a pressure tight seal between the internal passage and the surrounding environment. An isolation sleeve may be used to facilitate pressure testing of the seal.